Many methods for preparation of metal matrix composites containing carbon fibers have been attempted. The reason for this interest is because of the high strength of these fibers--3.5 to 6.5 GPa (500 to 970 ksi) with a specific gravity of 1.76 to 1.81. The specific high strength and modulus of these fibers have led to sales of over 15,000,000 lbs in epoxy and plastic composites. These fibers are around 7 micrometers in diameter and come with 3000, 6000 or 12000 filaments per tow wound onto spools. The fibers' main applications consist of epoxy composites used in aerospace and sporting goods.
The primary limiting characteristic of these organic matrix composites is their inability to function at temperatures much over 200.degree. C. For use at higher temperatures, researchers have developed methods to prepare carbon fiber composites utilizing an aluminum-based matrix. Methods discussed in prior literature include the following:
(a) liquid metal infiltration of aluminum around carbon fiber by squeeze casting; PA1 (b) physical vapor deposition, chemical vapor deposition, plasma spraying or electrolytic plating of aluminum onto carbon fibers and hot pressing the aluminum-coated carbon fibers; and PA1 (c) TiB.sub.2 or nickel coating a carbon fiber tow, then drawing the coated tow through molten aluminum and hot pressing the aluminum-coated tow. PA1 Pressure Infiltration--this has been used commercially to make Al.sub.2 O.sub.3 fiber composites. These techniques however, are less successful when applied to carbon fibers. Because molten aluminum does not wet carbon fibers, this process requires high infiltration pressures, increasing cost. One method to lower this high infiltration pressure is to use a nickel-coated carbon fiber preform as shown by Bell et al. in "Nickel-Coated Carbon Fiber Preforms for Metal Matrix Composites" 3rd International SAMPE Metals Processing Conference (1992), Vol. 24 (Advancements in Synthesis and Processes) Toronto, Canada, Oct. 20-22 (1992). The nickel coating allows the aluminum to easily wet the preform, thereby lowering the required infiltration pressure. While these alloys have some utility in high wear applications, this technique only incorporates a low volume fraction of fiber. Furthermore, this relatively low fiber content corresponds to a low composite strength. PA1 Carbon Fiber Tows--pre-coating these fibers with aluminum by ion plating, plasma spraying tows wound on a drum, electrolytic plating or chemical vapor deposition, each followed by hot pressing to form an article. PA1 Melt Drawing--pulling bundles of carbon fiber precoated with nickel into an aluminum matrix is also possible. Again, tows can be subsequently hot pressed together. The mechanical properties however do not reach those expected under the rule of mixtures due to the formation of an embrittling Al.sub.3 Ni phase.